Manufacturing of polyurethane flexible- and rigid foams, as well as of solid polyurethane elastomers are well-established industries. Recently, solid regid polyurethanes are becoming to be interesting.
Applications of polyurethane foams and elastomers are well known. As far as solid rigid polyurethanes are concerned they can be used as structural materials to replace metal, woods or other construction materials. Since their physical and mechanical properties can be tailored to suit the given requirements there are many possibilities for various outlets. The tailoring can also be done by applying fillers, which, in some cases, provide useful and appreciable properties. But there are some critical points for applying fillers with polyurethanes. The first one is the water content of fillers as well as of starting components for polyurethanes. To get polyurethanes without bubbles, water must be eliminated completely. The second point is the interfacial contact between resin and filler. This intimate contact is of course the essential problem of adhesion.
In up-to-date polyurethane systems fillers are added to polyols, not to poly-NCO-components.
In the procedure described in this invention the -NCO groups are brought in the immediate neighborhood of the filler by mixing both dry poly-NCO-component and filler in vacuo. In that way air and moisture are eliminated from the void spacing between asperities of both the macro- and microroughnesses of the filler. Only then electrostatical or molecular attraction between -NCO groups and active or activated sites of the filler, as well as chemical reaction between -NCO groups and, replaceable by sodium, active hydrogen of the filler can take place.
The activity and reactivity of an isocyanate are due to the chemical structure of the -NCO group, its configuration of electrons with their resonance possibilities: ##STR1## For the reason of the above mentioned attraction or reaction phenomenons an excess of the applied poly-NCO-component is needed. That excess is applied, basically, in accordance with the critical pigment volume concentration.